Properties of UIR Bands in NGC6946 Based on Mid-Infrared Imaging and Spectroscopy with Infrared Camera on Board AKARI

[摘要] Wepresentresultsonmid-infraredimagingandspectroscopicobservationsofthenearbylate-typespiralNGC6946withtheInfraredCameraonboardAKARI.Basedonmid-infraredimagingwiththeS7(7$$mu$$m)andS11(11$$mu$$m)bands,wefoundthattheS7/S11ratioshavelargervaluesinthearmregion,containingmanystar-formingregions,thanintheinterarm.Slitspectraofaninterarmandastar-formingregionshowaseriesofunidentifiedinfrared(UIR)bandsat6.2,7.7,8.6,and11.2$$mu$$m.Thestrengthsofthe6.2,7.7,and8.6$$mu$$mbandsarelargerrelativetothe11.2$$mu$$mbandinthestar-formingregion,thanintheinterarm,eveniftheinterstellarextinctionof$$A_V=3$$magtowardsthestar-formingregionistakenintoaccount.Theincreaseinthe6.2$$mu$$mand7.7$$mu$$mfeaturesrelativetothe11.2$$mu$$mfeatureisconsistentwiththeionizationmodelofPAHs.TheratiooftheUIRfeaturestotheplateauemissionunderthe7.7$$mu$$mand8.6$$mu$$mfeaturesand/ortheratioofthe7.6$$mu$$m/7.8$$mu$$mcomponentsinthe7.7$$mu$$mfeatureincreaseinthestar-formingregioncomparedtotheinterarm.Thisvariationcanbeaccountedforbythehypothesisthatthephoto-evaporationofPAHclustersproducesmallfree-flyingPAHsinthestar-formingregion.Theratiosof6.2$$mu$$m/11.2$$mu$$m,7.7$$mu$$m/11.2$$mu$$m,and8.6$$mu$$m/11.2$$mu$$mmaybetoolstomeasurethestar-formationactivityinremotegalaxiesiftheseratiosandtheirvariationsarewellexaminedandestablishedforalargesample.

[学科分类] 天文学(综合)

[关键词] "dust;extinction";"galaxies: individual (NGC 6946)";"galaxies: ISM";"galaxies: spirals";"infrared: galaxies"